1. Field of the Invention
The present invention relates to an electronic device such as a communication device and, in particular, relates to a housing structure of an electronic device having a sealed housing, and further to a heat radiation method therefor.
2. Description of the Related Art
With respect to a sealed housing used in an electronic device such as a communication device, a rise in temperature inside the housing is induced by heat generation from electrical circuit components mounted in a package or the like inside the housing, or due to a change in external environment. In order to suppress the rise in temperature to enhance reliability of an operation of the electronic device, the conventional sealed housing is provided with a heat radiation structure such as fins on the outer periphery of the housing. The heat radiation capacity of the housing is determined by a heat radiation effect of the heat radiation structure, and is so set as to exceed the total calorific value inside the housing. As the heat radiation structure, there is a cooling structure of an electronic device having an external heatsink exposed on the outer periphery of a sealed housing thereof, which is, for example, shown in FIG. 1 of JP-A-H10-154888.
On the other hand, in an electronic device having a sealed housing, when the temperature rises inside the housing, the atmospheric pressure inside the housing also increases, and therefore, a tetrafluoroethylene membrane filter (e.g. GORE-TEX), for example, may be attached to enhance reliability of an operation of the electronic device. Further, there is also such a housing that enhances reliability of an operation of an electronic device by employing a tube containing water to thereby suppress a change in atmospheric pressure, which is, for example, described in JP-A-H07-176877.
However, when, for example, the membrane filter is used, if water vapor or poisonous gas invades from the exterior passing through the membrane filter, dew condensation is resulted inside the housing. Consequently, there has been a problem of occurrence of a phenomenon such as corrosion of electrical circuit components inside the housing. On the other hand, if the tube containing water is employed for solving it, there has been a problem that no effect is achieved when the water is vaporized.